1. Field of the Invention
The present invention relates to a plenum fan banding. More specifically the present invention employs a removable and replaceable band that attaches to the back of a fan wheel so that the band extends outward perpendicular to the back of the wheel. Addition of the band to the back of the fan wheel changes the effective width of the fan wheel, thereby allowing the output of the fan, which is direct driven by a single speed motor, to be finely adjusted or trimmed to match the performance of the HVAC unit in which it is employed.
2. Description of the Related Art
It is desirable to match the performance of a plenum fan to the performance of the HVAC unit with which the fan is employed. Currently, there are two methods that are commonly employed to fine adjust or trim the plenum fan so that its performance can be matched to that of its associated HVAC unit.
The first of these two current methods for trimming a plenum fan is to employ a variable speed drive motor to drive the plenum fan instead of directly driving the fan with a single speed motor. A variable speed drive motor is more expensive to install than a single speed drive motor and a variable speed drive motor is more expensive to service. Also, one must be careful to use a variable speed or variable frequency drive (VFD) compatible motor.
The second of these two current methods for trimming a plenum fan is to adjust the width of the wheel of the fan. This requires that the wheel be replaced with another wheel of a different width, a process that is expensive and time consuming.
Other ways that the output of plenum fans have been adjusted include retracting the fan inlet funnel or otherwise restricting air flow going to the fan, changing the pitch of the fan blades, employing fan blades that can be adjusted outwardly, and moving the fan blades inward and outward relative to the fan housing.
Each of these methods has its own unique problems. The present invention addresses these problems by providing plenum fan banding that effectively changes the width of the fan blades without having to replace the fan or made major modifications to it. The present invention employs a removable and replaceable band that attaches to the back of a fan wheel so that the band extends outward perpendicular to the back of the wheel. This band can be constructed of a strip of sheet metal that is fastened at its ends to form a hoop of a uniform width. Several tabs are provided on one edge of the strip so that when that edge of the strip is facing the back of the fan wheel, the tabs can be inserted through slots provided in the back of the fan wheel as a means of securing the band to the fan wheel.
Once the tabs are fully inserted in their respective slots, the tabs are bent over, thereby holding the band securely to the fan wheel. When thus attached to the fan wheel, the band extends perpendicular to the back of the fan wheel and is located inside or within the circle of fan blades. By attaching the band to the fan wheel in this manner, the band changes the effective width of the fan wheel, thereby allowing the output of the fan, which is direct driven by a single speed motor, to be finely adjusted or trimmed to match the performance of the HVAC unit in which it is employed.
Also, because the band is attached by tabs to the back of the fan, by simply straightening the tabs back out, the tabs can be removed from the slots to thereby remove the band so that the band can be replaced by another band of a different width to again change the effective width of the fan blades and adjust the resulting output of the plenum fan.